Exciplex spin-flip acceleration enables high-performance narrowband electroluminescence.

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Thermally activated delayed fluorescence (TADF) in organic light-emitting diodes (OLEDs) utilizes triplet excitons for enhanced emission.
• Reverse intersystem crossing (RISC) is crucial for harvesting triplet excitons but is often a bottleneck in TADF systems.

Purpose of the Study:

• To develop novel exciplex systems with enhanced RISC rates for improved OLED performance.
• To investigate the role of heavy atoms in localizing triplet states and increasing spin-orbit coupling.

Main Methods:

• Incorporation of heavy atoms into exciplex-forming systems.
• Positional isomer optimization to fine-tune electronic properties.
• Fabrication and characterization of OLED devices using the developed exciplex hosts.

Main Results:

• Achieved a RISC rate constant of 4.9 × 10^6 s^-1, an order of magnitude higher than typical exciplexes.
• Demonstrated OLEDs with a maximum external quantum efficiency (EQE) exceeding 40%.
• Observed minimal efficiency roll-off, with EQE remaining above 33% at 1000 cd m^-2.

Conclusions:

• Heavy-atom incorporation significantly enhances RISC in exciplexes, enabling efficient TADF.
• Optimized heavy-atom exciplexes are promising hosts for high-performance, stable OLEDs.